1. Field of the Invention
This invention relates to a novel process for preparing adenine starting from diaminomaleonitrile (hereinafter called "DAMN") and/or diaminofumaronitrile (hereinafter called "DAFN").
2. Description of the Prior Art
Adenine is widely present in tissues of animals and plants as a main constituent of nucleic acids and coenzymes and plays an important role. Adenine and its derivatives are known as having pharmacological effects and are very useful in medical and biochemical fields. Furthermore, adenine is an important intermediate for preparing 5'-nucleotides, used as seasoning.
There have been, heretofore, proposed several dozens of methods including the methods used only in the laboratory, for preparing adenine. As commercial one step methods, there are, for example, a method comprising reacting hydrogen cyanide or other cyanide with ammonia or an ammonium salt substantially in the absence of moisture (Japanese Patent Publication No. 10113/1966) and a method comprising reacting formamide with an acid anhydride derived from phosphorus or sulfur, or acid halide (Japanese Patent Publication No. 6955/1968). However, in the former there is used hydrogen cyanide, a very poisonous compound, under high pressure and a lot of by-products are formed, as are, insoluble colored matter produced by polymerization of hydrogen cyanide. In view of the foregoing, the former is not satisfactory as a commercial process.
In the latter, an acid anhydride or acid halide should be used so that highly corrosion-resistant materials are necessary and consequently the commercial plant is very expensive. In addition, a lot of by-products, acidic products derived from phosphorous of sulfur compounds, should be treated and the reaction should be carried out under pressure. Therefore, neither is the latter satisfactory as a commercial process. For improving the above methods, there have been proposed methods comprising reacting an amidine salt with DAMN or DAFN, for example, those disclosed in Japanese Patent Publication Nos. 4374/1971 and 20623/1972. DAMN can be easily and safely produced from hydrogen cyanide and DAFN can be easily derived from DAMN.
In the above mentioned methods, the reaction procedure is easy and safe and complicated by-products are not produced so that adenine can be easily isolated. However, in these methods an amidine salt is used as one of the starting materials. The amidine salt is a special organic chemical material which is not commercially available. Even if it were commercially available, it would be very expensive. Further it is described that the presence of even a small amount of ammonia in the reaction system decreases the yield of adenine. In view of the foregoing these methods are not commercially satisfactory.